1. Field of the Invention
The present invention relates to a connecting structure for exhaust pipes of an engine, and more particularly to a connecting structure between a plurality of parallel upstream exhaust pipes located downstream of an exhaust manifold and a plurality of parallel downstream exhaust pipes arranged so as to correspond to the upstream exhaust pipes, respectively.
2. Description of the Related Art
Conventionally, in exhaust pipes of an automotive engine, there has been known to the public an exhaust pipe connecting structure having a first connecting flange, and a second connecting flange. The first connecting flange is connected to peripheries of downstream-end portions of a plurality of parallel upstream exhaust pipes in such a manner as to extend over the downstream end portions of the upstream exhaust pipes. The second connecting flange is connected to peripheries of upstream-end portions of a plurality of parallel downstream exhaust pipes, arranged so as respectively to correspond to the upstream exhaust pipes, in such a manner as to extend over the upstream end portions of the downstream exhaust pipes. Further, a plurality of spherical joints is provided between the two connecting flanges for airtightly connecting the downstream-ends of the upstream exhaust pipes with respective upstream-ends of the downstream exhaust pipes. Each of the spherical joints includes an annular seal unit having a central opening for passage of exhaust gas, wherein each annular seal unit is held in place between the fist and second connecting eflangcs. Still further, spherical bearing surfaces are formed on one of the connecting flanges in such a manner as to be brought into slidable spherical contact with respective spherical portions formed on one side of each annular seal unit so as to surround the central opening. Additionally, elastic retaining means is provided between the two connecting flanges for elastically pressing the spherical bearingy surfaces against the spherical portions of the annular seal units (refer, for example, to FIG. 2 of JP-A-9-144534).
In this conventional structure, the upstream and downstream exhaust pipes can be bent relative to each other around an axis connecting, the spherical centers of the respective spherical joints, and the structure can be advantageous in permitting the swing of an engine in a specific direction with less effort, or advantageous in preventing the transmission of engine vibrations to a muffler or mufflers.
With the conventional structure, the first and second connecting flanges are formed integrally with the plurality of spherical joints in such a manner as to extend thereover. For example, the second connecting flange includes spherical bearing surfaces for holding the spherical joints. The conventional structure can be advantageous in reducing, the number of components to be used, but the annular seal units fit, respectively, on the peripheries of the end portions of the exhaust pipes extending from the first connecting flangexe2x80x94which has no spherical bearingy surfacesxe2x80x94without looseness. Therefore, because the exhaust pipes are mounted such that no slide of the annular seal units is permittedxe2x80x94in a direction normal to the axes of the exhaust pipesxe2x80x94elative to the bearing, surfaces of the connecting flanges, and/or because the pipes are mounted in a state in which the center axes thereof are fixed, the following problems result.
When, due to the production tolerance, a distance between the centers of respective mounting positions of the plurality of upstream exhaust pipes on the first connecting flange does not match a distance between the centers of respective mounting positions of the plurality of downstream exhaust pipes on the second connecting flange, the seal units are forced to bear unbalanced loads so as to be subjected to a large, lateral, unnatural, strain deformation. The large strain deformation results from the seal unit""s location between the end portions of the exhaust pipes, on which the seal units are fitted, and the spherical bearing surface corresponding to the seal units. This large strain deformation leads to a risk of exhaust-gas leakage. Additionally, in order to avoid the above-described problem caused by the discord in distance between the centers of mounting positions, a high accuracy is required for production of both the upstream and downstream exhaust pipes. And the requirement for high accuracy leads to an increase in production cost.
With a view to solving the above problem, JP-A-9-317461 describes a connecting structure in which one of the connecting flanges-the one which has the spherical bearing surfacesxe2x80x94is formed with separate components for the respective spherical bearing surfaces, while the other connecting flange remains an integral component used commonly for the plurality of spherical joints. However, in order to reduce the number and weight of components involved, and in order to reduce production costs, it is desirable that each of the connecting flanges is formed as one piece which extends over the plurality of spherical joints.
The present invention was made in view of the above circumstances, and an object thereof is to provide a connecting structure for exhaust pipes in which each first and second connecting flanges is formed as an integral component extending over a plurality of spherical joints, and in which high production accuracy is not required.
With a view to attaining, the above and other objects, a first aspect of the invention provides a connecting structure for exhaust pipes including a first connecting flange, a second connecting flange, and a plurality of spherical joints. The first connecting flange is connected to peripheries of downstream-end portions of a plurality of parallel upstream exhaust pipes in such a manner as to extend over the downstream-end portions of the upstream exhaust pipes. The second connecting flange is connected to peripheries of upstream-end portions of a plurality of parallel downstream exhaust pipesxe2x80x94arranged so as to correspond to the upstream exhaust pipes, respectivelyxe2x80x94in such a manner as to extend over the upstream-end portions of the downstream exhaust pipes. And the plurality of spherical joints is disposed between the two connecting flanges for airtightly connecting downstream-ends of the upstream exhaust pipes with respective upstream-ends of the downstream exhaust pipes. Each of the spherical joints includes an annular seal unit having a central opening for passage of exhaust gas, the annular seal units being held in place between the fist and second connecting flanges.
Further, spherical bearing, surfaces arc formed on one of the connecting flanges so as to be brought into slidable spherical contact with spherical portions formed on respective annular seal units. The spherical bearing, surfaces also surround respective central opening,s in the annular seal units. Additionally, flat bearing surfaces are formed on the other connecting flange so as to confront the respective seal units, and so as to be in relatively slidable contact therewith in a direction substantially normal to longitudinal axes of the respective exhaust pipes.
According to the above feature, when the distance between centers of mounting, positions of the plurality of respective upstream exhaust pipes to the first connecting flange does not match the distance between centers of mounting position of the plurality of respective downstream pipes to the second connecting flangexe2x80x94due to production errors or the likexe2x80x94the plurality of annular seal units is held in place between the two connecting flanges so that the fiat sides of respective seal units are allowed to slide on the flat bearing surfaces of the other connecting flange without any strain. Therefore, it is possible to effectively prevent the seal units from being subjected to unbalanced transversal loads between the two connecting flanges and, thereby, strain deformed. Therefore, the connecting structure for exhaust pipes according to the present invention is less likely to have gas leakage, and no high manufacturing precision is required for production of the connecting flanges and exhaust pipes.
Additionally, each of the first and second connecting flanges can be formed integrally in such a manner as to extend over the plurality of spherical joints, whereby the number of components is reduced and, hence, the weight and costs of the connecting structure is also reduced.
Moreover, because of the sliding displacement of the respective annular seal units on the flat bearing surfaces of the other connecting flange, the upstream and downstream exhaust pipes are allowed to flex relative to one another. That is, the upstream and downstream exhaust pipes can flex relative to one another about the axis connecting the spherical centers of the spherical joints. The axis connecting the spherical centers of the spherical bearing surfaces can be displaced in various directions along the flat bearing surfaces relative to the other connecting flange, whereby even if the rocking axis or rolling axis of the engine is displaced, the upstream and downstream exhaust pipes are allowed to flex relative to one another. This flexure is important because the rocking or rolling axis of the entwine may be displaced in response to a change in operating condition, for example, when there is being generated a driving reaction force, a change in weight of the engine itself in conjunction with change in oil volume therein, or when the vehicle is being inclined. Because the upstream and downstream exhaust pipes are allowed to flex relative to each other in accordance with such a displacement, it is possible to effectively absorb the rocking and rolling displacement of the engine without strain.
According to a second aspect of the invention, there is provided a connecting structure for exhaust pipes as set forth in the first aspect of the invention, and further wherein:
for each spherical joint, an annular extended portion is integrally formed on one of the upstream exhaust pipes, the downstream exhaust pipes, the first connecting flange, and the second connecting flange, the annular extended portion being disposed in the central opening, and
a diametrical gap is formed between an outer peripheral surface of the extended portion and an inner circumferential surface of the central opening, the is diametrical gap permitting the sliding movement of the annular seal unit.
According to this aspect of the present invention, the heat shielding effect of the extended portions prevents the exposure of the annular seal units to exhaust gas and, hence, suppresses the early deterioration thereof by heat. However, even with the annular extended portions being so provided, the seal units are allowed to slide for displacement without any difficulty because their flat sides engage the fiat bearing(g surfaces of the other connecting flange, and they are not disturbed by the extended portions.
According to a third aspect of the invention, there is provided a connecting structure for exhaust pipes as set forth in the first aspect of the invention, wherein each of the spherical joints further includes:
a cylindrical heat shielding member fitted in and secured to an inner circumferential surface of the central opening of the annular seal unit; and
a space adjacent to an inner circumferential side of the heat shielding member, wherein the space permits the sliding, movement of the annular seal unit.
According to this aspect of the present invention, the extended portions do not always need to be provided on the connecting flanges or the exhaust pipes, thereby increasing the degree of freedom in designing the components.